Radar detection circuit for a WLAN transceiver

ABSTRACT

A single chip radio transceiver includes circuitry that enables detection of radar signals to enable the radio transceiver to halt communications in overlapping communication bands to avoid interference with the radar transmitting the radar pulses. One design goal, however, is to avoid false triggers that result from spurious tones and omissions and that further detects radar signals even in circumstances in which a radar pulse has been masked or eliminated by interference. Accordingly, the radar detection block includes circuitry for detecting and measuring the radar signals in the presence of such interference. More specifically, the radar detection block includes a moving average filter, a threshold comparison state machine, and radar detection logic within software that is executed by a processor for determining whether a radar signal is present.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 60/502,934, filed Sep. 15, 2003, which is incorporated hereinby reference for all purposes.

BACKGROUND

1. Technical Field

The present invention relates to wireless communications and, moreparticularly, wideband wireless communication systems.

2. Related Art

Communication systems are known to support wireless and wire linedcommunications between wireless and/or wire lined communication devices.Such communication systems range from national and/or internationalcellular telephone systems to the Internet to point-to-point in-homewireless networks. Each type of communication system is constructed, andhence operates, in accordance with one or more communication standards.For instance, wireless communication systems may operate in accordancewith one or more standards, including, but not limited to, IEEE 802.11,Bluetooth, advanced mobile phone services (AMPS), digital AMPS, globalsystem for mobile communications (GSM), code division multiple access(CDMA), local multi-point distribution systems (LMDS),multi-channel-multi-point distribution systems (MMDS), and/or variationsthereof.

Depending on the type of wireless communication system, a wirelesscommunication device, such as a cellular telephone, two-way radio,personal digital assistant (PDA), personal computer (PC), laptopcomputer, home entertainment equipment, etc., communicates directly orindirectly with other wireless communication devices. For directcommunications (also known as point-to-point communications), theparticipating wireless communication devices tune their receivers andtransmitters to the same channel or channels (e.g., one of a pluralityof radio frequency (RF) carriers of the wireless communication system)and communicate over that channel(s). For indirect wirelesscommunications, each wireless communication device communicates directlywith an associated base station (e.g., for cellular services) and/or anassociated access point (e.g., for an in-home or in-building wirelessnetwork) via an assigned channel. To complete a communication connectionbetween the wireless communication devices, the associated base stationsand/or associated access points communicate with each other directly,via a system controller, via a public switched telephone network (PSTN),via the Internet, and/or via some other wide area network.

Each wireless communication device includes a built-in radio transceiver(i.e., receiver and transmitter) or is coupled to an associated radiotransceiver (e.g., a station for in-home and/or in-building wirelesscommunication networks, RF modem, etc.). As is known, the transmitterincludes a data modulation stage, one or more intermediate frequencystages, and a power amplifier. The data modulation stage converts rawdata into baseband signals in accordance with the particular wirelesscommunication standard. The one or more intermediate frequency stagesmix the baseband signals with one or more local oscillations to produceRF signals. The power amplifier amplifies the RF signals prior totransmission via an antenna.

As is also known, the receiver is coupled to the antenna and includes alow noise amplifier, one or more intermediate frequency stages, afiltering stage, and a data recovery stage. The low noise amplifierreceives an inbound RF signal via the antenna and amplifies it. The oneor more intermediate frequency stages mix the amplified RF signal withone or more local oscillations to convert the amplified RF signal into abaseband signal or an intermediate frequency (IF) signal. As usedherein, the term “low IF” refers to both baseband and intermediatefrequency signals. A filtering stage filters the low IF signals toattenuate unwanted out of band signals to produce a filtered signal. Thedata recovery stage recovers raw data from the filtered signal inaccordance with the particular wireless communication standard.

One approach to using a higher intermediate frequency is to convert theRF signal to an intermediate frequency sufficiently low to allow theintegration of on-chip channel selection filters. For example, somenarrow band or low data rate systems, such as Bluetooth, use this lowintermediate frequency design approach.

Active mixers used in direct conversion radios, as well as radios thatemploy an intermediate conversion step, typically comprise inputtransconductance elements, switches and an output load. These activemixers often have varying output signal characteristics due toenvironmental conditions, such as temperature, and process andmanufacturing variations. These varying output signal characteristicscan, for example, result in a mixer producing an errant localoscillation signal that affects the accuracy of an output signal'sfrequency. Having inaccurate output frequencies can result in manyundesirable outcomes, including unwanted signal filtering by adownstream filter.

Other approaches are also being pursued to achieve the design goal ofbuilding entire radios on a single chip. With all of the foregoingdesign goals, however, there is being realized an increasing need foradditional frequency bands for use by radio receivers and transmittersof all types. Along these lines, a frequency band that has heretoforebeen reserved exclusively for radar systems is being opened for use forat least some types of wireless communication systems. Among othersystems, wireless local area network (LAN) systems are being developedto take advantage of the frequency band that is being opened up whichhas been reserved for radar. One design issue, however, that accompaniesany wireless LAN device that operates in this frequency band is that ofcoexistence with radar systems. More specifically, a need exists for awireless LAN transceiver to give priority to a radar when a radaroperation is detected. Accordingly, the wireless LAN, in such ascenario, would be required to detect a radar signal within a specifiedresponse time and to communicate over a non-overlapping frequency bandthereto.

Along these lines, recent changes to government regulations will allowwireless LANs (WLANs) to share frequency spectrum with licensed radarsystems. Specifically, the frequency bands 5.25-5.35 GHz and 5.47-5.75GHz will be open in Europe, and perhaps worldwide at some point in thefuture. Since these frequency bands are shared, the wireless LANs willbe required to take a subordinate role to the licensed radar systems.This includes the incorporation of dynamic frequency selection (DFS)within the WLAN that will avoid spectrum that is occupied by a radar.What is needed, therefore, is a circuit and method for determining whena radar signal is present.

SUMMARY OF THE INVENTION

One embodiment of the present invention includes a radio receiver thatfurther includes front-end circuitry for receiving, amplifying,down-converting and filtering an RF signal, and circuitry for convertingthe received down-converted, amplified and filtered RF signal into adigital signal and further includes a radar detection block (circuit)that monitors the incoming digital signals to detect the presence ofradar. Generally, the radar signal includes a plurality of equallyspaced pulses having a magnitude that is significantly greater than amagnitude of a signal transmitted according to any one of the various802.11 protocols (though the invention includes any wireless LANprotocol in use). One design goal, however, is to avoid false triggersthat result from spurious tones and omissions and that further detectsradar signals even in circumstances in which a radar pulse has beenmasked or eliminated by interference. Accordingly, the radar detectionblock includes circuitry for detecting and measuring the radar signalsin the presence of such interference. More specifically, the radardetection block includes a moving average filter, a threshold comparisonstate machine, and radar detection logic within software that isexecuted by a processor for determining whether a radar signal ispresent. A threshold comparison state machine measures the rise time andmagnitude of an incoming signal. A radar signal typically generates apattern of threshold crossings that, when interpreted by a processor,would yield data to facilitate the radio receiver being able to reach aconclusion that a radar signal is present. Accordingly, the radioreceiver communicates with logic within the radio transceiver to inhibittransmissions in frequency bands that overlap the frequency bands of theradar signal.

A typical wireless LAN receiver, such as used to implement the 802.11astandard, is not capable of detecting the short, regular pulses of aradar system. This invention includes, therefore, additional circuitryto the wireless LAN receiver circuitry to enable radar pulse detection.There are three main components: a power detector circuit, a statemachine, and a software-driven processor. The power detector circuittaps the received signal off the main path and computes the magnitudesquared of the incoming (full bandwidth) signal. The output of the powerdetector circuit is applied to the state machine, which compares theinstantaneous power to two different thresholds. This mechanism allowsthe measurement of the radar pulse start time, rise time, pulse width,and fall time. The state machine records these parameters into a pulsebuffer. The software processor reads the pulse buffer and performsfurther processing as necessary to determine whether or not a radar ispresent.

Other aspects of the present invention will become apparent with furtherreference to the drawings and specification, which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description of the preferred embodiment is consideredwith the following drawings, in which:

FIG. 1 is a functional block diagram illustrating a communication systemthat includes a plurality of base stations and/or access points, aplurality of wireless communication devices and a network hardwarecomponent;

FIG. 2 is a schematic block diagram illustrating a wirelesscommunication device as a host device and an associated radio;

FIG. 3 is a functional schematic diagram of a direct conversion radiotransceiver formed according to one embodiment of the present invention;

FIG. 4 is a functional schematic diagram of an automatic frequencycontrol (AFC) circuit formed according to one described embodiment ofthe invention;

FIG. 5 is a diagram that illustrates the relative difference between aradar signal waveform and an 802.11 wireless LAN waveform signal;

FIG. 6 is a signal diagram illustrating two groups of pulses of a radarsignal;

FIG. 7 is a diagram that illustrates the measurement of rise time andfall time of the pulses of the radar signal;

FIG. 8 is a functional block diagram of a portion of a radio transceiveraccording to one embodiment of the present invention;

FIG. 9 is a functional block diagram of a radar detection block for usein an 802.11a receiver formed according to one embodiment of the presentinvention;

FIG. 10 is a diagram illustrating signal waveforms for radar pulses and802.11a signals;

FIG. 11 is a functional block diagram of a moving average block asemployed in one embodiment of the present invention;

FIG. 12 illustrates a threshold comparison state machine; and

FIG. 13 is a flowchart illustrating a series of steps that are performedaccording to one embodiment of the present invention;

FIG. 14 is a flowchart illustrating a method for determining whether aradar signal is present according to one embodiment of the invention;

FIG. 15 is a flowchart illustrating a method for performing radardetection processing;

FIG. 16 is a flowchart illustrating a method for performing radardetection processing for missing pulses;

FIG. 17 is a flowchart illustrating a method for performing radardetection processing for extra pulses; and

FIGS. 18, 19, and 20 illustrate the generation of data that is utilizedin the described embodiments of the invention for determining whether aradar is present.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram illustrating a communication system10 that includes a plurality of base stations or access points (AP)12-16, a plurality of wireless communication devices 18-32 and a networkhardware component 34. The wireless communication devices 18-32 may belaptop host computers 18 and 26, personal digital assistant hosts 20 and30, personal computer hosts 24 and 32 and/or cellular telephone hosts 22and 28. The details of the wireless communication devices will bedescribed in greater detail with reference to FIG. 2. In one embodimentof the present invention, every access point 12-16 and every wirelesscommunication device 18-32 that is operable to communicate in the radarbands described herein is capable of detecting radar signals and tocease communicating in radar bands so long as a signal is present. In analternate embodiment of the invention, the various access points 12-16are capable of detecting a radar and further to communicate with any ofthe wireless communication devices 18-32 to prompt the wirelesscommunication devices 18-32 to cease transmitting in the radar band inwhich radar is detected. Accordingly, one or more of the wirelesscommunication devices 18-32 is operable to cease communications in theradar band based upon the received prompt from the wirelesscommunication device 12-16.

The base stations or AP 12-16 are operably coupled to the networkhardware component 34 via local area network (LAN) connections 36, 38and 40. The network hardware component 34, which may be a router,switch, bridge, modem, system controller, etc., provides a wide areanetwork connection 42 for the communication system 10. Each of the basestations or access points 12-16 has an associated antenna or antennaarray to communicate with the wireless communication devices in itsarea. Typically, the wireless communication devices 18-32 register withthe particular base station or access points 12-16 to receive servicesfrom the communication system 10. For direct connections (i.e.,point-to-point communications), wireless communication devicescommunicate directly via an allocated channel.

Typically, base stations are used for cellular telephone systems andlike-type systems, while access points are used for in-home orin-building wireless networks. Regardless of the particular type ofcommunication system, each wireless communication device includes abuilt-in radio and/or is coupled to a radio.

FIG. 2 is a schematic block diagram illustrating a wirelesscommunication device 18-32 as a host device and an associated radio 60.For cellular telephone hosts, the radio 60 is a built-in component. Forpersonal digital assistants hosts, laptop hosts, and/or personalcomputer hosts, the radio 60 may be built-in or an externally coupledcomponent.

As illustrated, the host wireless communication device 18-32 includes aprocessing module 50, a memory 52, a radio interface 54, an inputinterface 58 and an output interface 56. The processing module 50 andmemory 52 execute the corresponding instructions that are typically doneby the host device. For example, for a cellular telephone host device,the processing module 50 performs the corresponding communicationfunctions in accordance with a particular cellular telephone standard.

The radio interface 54 allows data to be received from and sent to theradio 60. For data received from the radio 60 (e.g., inbound data), theradio interface 54 provides the data to the processing module 50 forfurther processing and/or routing to the output interface 56. The outputinterface 56 provides connectivity to an output device such as adisplay, monitor, speakers, etc., such that the received data may bedisplayed. The radio interface 54 also provides data from the processingmodule 50 to the radio 60. The processing module 50 may receive theoutbound data from an input device such as a keyboard, keypad,microphone, etc., via the input interface 58 or generate the dataitself. For data received via the input interface 58, the processingmodule 50 may perform a corresponding host function on the data and/orroute it to the radio 60 via the radio interface 54.

Radio 60 includes a host interface 62, a digital receiver processingmodule 64, an analog-to-digital converter 66, a radar detection block67, a filtering/gain module 68, a down-conversion module 70, a a lownoise amplifier 72, receiver filter module 71, a transmitter/receiver(Tx/Rx) switch module 73, a local oscillation module 74, a memory 75, adigital transmitter processing module 76, a digital-to-analog converter78, a filtering/gain module 80, an IF mixing up-conversion module 82, apower amplifier 84, a transmitter filter module 85, and an antenna 86.The antenna 86 is shared by the transmit and receive paths as regulatedby the Tx/Rx switch module 73. The antenna implementation will depend onthe particular standard to which the wireless communication device iscompliant.

The radar detection block 67 is operable to receive a digital lowfrequency signal from ADC 66 and to process such digital low frequencysignal to determine whether a radar signal is present. Radar detectionblock 67, upon detecting a radar signal, prompts radio 60 to inhibitcommunications in frequency bands that overlap with radar and, in thecase of ongoing communications, to switch outgoing communications to anon-overlapping frequency band (non-overlapping with radar).

The digital receiver processing module 64 and the digital transmitterprocessing module 76, in combination with operational instructionsstored in memory 75, execute digital receiver functions and digitaltransmitter functions, respectively. The digital receiver functionsinclude, but are not limited to, demodulation, constellation demapping,decoding, and/or descrambling. The digital transmitter functionsinclude, but are not limited to, scrambling, encoding, constellationmapping, modulation. The digital receiver and transmitter processingmodules 64 and 76 may be implemented using a shared processing device,individual processing devices, or a plurality of processing devices.Such a processing device may be a microprocessor, micro-controller,digital signal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on operationalinstructions. The memory 75 may be a single memory device or a pluralityof memory devices. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, and/or any device that storesdigital information. Note that when the digital receiver processingmodule 64 and/or the digital transmitter processing module 76 implementsone or more of its functions via a state machine, analog circuitry,digital circuitry, and/or logic circuitry, the memory storing thecorresponding operational instructions is embedded with the circuitrycomprising the state machine, analog circuitry, digital circuitry,and/or logic circuitry. The memory 75 stores, and the digital receiverprocessing module 64 and/or the digital transmitter processing module 76executes, operational instructions corresponding to at least some of thefunctions illustrated herein.

In operation, the radio 60 receives outbound data 94 from the hostwireless communication device 18-32 via the host interface 62. The hostinterface 62 routes the outbound data 94 to the digital transmitterprocessing module 76, which processes the outbound data 94 in accordancewith a particular wireless communication standard (e.g., IEEE 802.11a,IEEE 802.11b, Bluetooth, etc.) to produce digital transmission formatteddata 96. The digital transmission formatted data 96 will be a digitalbaseband signal or a digital low IF signal, where the low IF typicallywill be in the frequency range of one hundred kilohertz to a fewmegahertz.

The digital-to-analog converter 78 converts the digital transmissionformatted data 96 from the digital domain to the analog domain. Thefiltering/gain module 80 filters and/or adjusts the gain of the analogbaseband signal prior to providing it to the up-conversion module 82.The up-conversion module 82 directly converts the analog basebandsignal, or low IF signal, into an RF signal based on a transmitter localoscillation 83 provided by local oscillation module 74. The poweramplifier 84 amplifies the RF signal to produce an outbound RF signal98, which is filtered by the transmitter filter module 85. The antenna86 transmits the outbound RF signal 98 to a targeted device such as abase station, an access point and/or another wireless communicationdevice.

The radio 60 also receives an inbound RF signal 88 via the antenna 86,which was transmitted by a base station, an access point, or anotherwireless communication device. The antenna 86 provides the inbound RFsignal 88 to the receiver filter module 71 via the Tx/Rx switch module73, where the Rx filter module 71 bandpass filters the inbound RF signal88. The Rx filter module 71 provides the filtered RF signal to low noiseamplifier 72, which amplifies the inbound RF signal 88 to produce anamplified inbound RF signal. The low noise amplifier 72 provides theamplified inbound RF signal to the down-conversion module 70, whichdirectly converts the amplified inbound RF signal into an inbound low IFsignal or baseband signal based on a receiver local oscillation signal81 provided by local oscillation module 74. The down-conversion module70 provides the inbound low IF signal or baseband signal to thefiltering/gain module 68. The filtering/gain module 68 may beimplemented in accordance with the teachings of the present invention tofilter and/or attenuate the inbound low IF signal or the inboundbaseband signal to produce a filtered inbound signal.

The analog-to-digital converter 66 converts the filtered inbound signalfrom the analog domain to the digital domain to produce digitalreception formatted data 90. The digital receiver processing module 64decodes, descrambles, demaps, and/or demodulates the digital receptionformatted data 90 to recapture inbound data 92 in accordance with theparticular wireless communication standard being implemented by radio60. The host interface 62 provides the recaptured inbound data 92 to thehost wireless communication device 18-32 via the radio interface 54.

As one of average skill in the art will appreciate, the wirelesscommunication device of FIG. 2 may be implemented using one or moreintegrated circuits. For example, the host device may be implemented ona first integrated circuit, while the digital receiver processing module64, the digital transmitter processing module 76 and memory 75 areimplemented on a second integrated circuit, and the remaining componentsof the radio 60, less the antenna 86, may be implemented on a thirdintegrated circuit. As an alternate example, the radio 60 may beimplemented on a single integrated circuit. As yet another example, theprocessing module 50 of the host device and the digital receiverprocessing module 64 and the digital transmitter processing module 76may be a common processing device implemented on a single integratedcircuit. Further, memory 52 and memory 75 may be implemented on a singleintegrated circuit and/or on the same integrated circuit as the commonprocessing modules of processing module 50, the digital receiverprocessing module 64, and the digital transmitter processing module 76.

The wireless communication device of FIG. 2 is one that may beimplemented to include either a direct conversion from RF to basebandand baseband to RF or for a conversion by way of a low intermediatefrequency. In either implementation, however, for an up-conversionmodule 82 and a down-conversion module 70, it is required to provideaccurate frequency conversion. For the down-conversion module 70 andup-conversion module 82 to accurately mix a signal, however, it isimportant that the local oscillation module 74 provide an accurate localoscillation signal for mixing with the baseband or RF by theup-conversion module 82 and down-conversion module 70, respectively.Accordingly, the local oscillation module 74 includes circuitry foradjusting an output frequency of a local oscillation signal providedtherefrom. As will be explained in greater detail, below, the localoscillation module 74 receives a frequency correction input that it usesto adjust an output local oscillation signal to produce a frequencycorrected local oscillation signal output. While one embodiment of thepresent invention includes local oscillation module 74, up-conversionmodule 82 and down-conversion module 70 that are implemented to performdirect conversion between baseband and RF, it is understand that theprinciples herein may also be applied readily to systems that implementan intermediate frequency conversion step at a low intermediatefrequency.

FIG. 3 is a functional schematic diagram of a direct conversion radiotransceiver formed according to one embodiment of the present invention.Referring now to FIG. 3, a transceiver system comprises radio circuitry304 that is coupled to baseband processing circuitry 308. The radiocircuitry 304 performs filtering, amplification, frequency calibration(in part) and frequency conversion (down from the RF to baseband and upfrom baseband to the RF). Baseband processing circuitry 308 performs thetraditional digital signal processing in addition to partiallyperforming the automatic frequency control. As may be seen, the singlechip radio circuitry 304 is coupled to receive radio signals that areinitially received by the transceiver and then converted by a Balunsignal converter, which performs single end to differential conversionfor the receiver (and differential to single end conversion for thetransmitter end). The Balun signal converters are shown to be off-chipin FIG. 3, but they may be formed on-chip with radio circuitry 304 aswell. Similarly, while the baseband processing circuitry 308 is shownoff-chip, it also may be formed on-chip with radio circuitry 304.

Radio circuitry 304 and, more particularly, circuitry portion 304A,includes a low noise amplifier 312 that is coupled to receive RF signalsfrom a transceiver port. The low noise amplifier 312 then produces anamplified signal to mixers 316 that are for adjusting and mixing the RFwith a local oscillation signal. The outputs of the mixers 316 (I and Qcomponents of quadrature phase shift keyed signals) are then produced toa first HP-VGA 320.

The outputs of the first HP-VGA 320 are then produced to a first RSSI328 as well as to a low pass filter 324. The outputs of the low passfilter 324 are then produced to a second RSSI 332, as well as to asecond HP-VGA 336 and a third HP-VGA 340 as may be seen in FIG. 3. Theoutputs of HP-VGA 340 are then produced to a pair of analog-to-digitalconverters. The analog-to-digital converters then produce digital datato both radar detection block 342 and a digital block for processing.Radar detection block 342 is operable to monitor incoming signals anddetermine when a radar signal is present. In one embodiment, radardetection block 342 produces an indication that a radar is present(shown as RADAR DETECT CONTROL SIG. in FIG. 3) to the digital blockwhich the takes specified actions including suspending transmissions inoverlapping radar channels. It is understood that the RADAR DETECTCONTROL SIG. may merely be a binary control signal in one embodiment toprompt the digital block to inhibit transmission or it may be pulse datawhere logic within the digital block evaluates the pulse data todetermine whether a radar has been detected. Moreover, as may be seen,radar detection block 342 receives digital low frequency signals fromthe ADCs. In an alternate embodiment, however, the radar detection blockincludes its own set of ADCs and receives low frequency analog signalsfrom the inputs of the ADC. Such alternate embodiment may be implementedas a matter of design choice.

First RSSI 328 measures the power level of the signal and interference.The second RSSI 332 measures the power level of the signal only. Thebaseband processing circuitry 308 then determines the ratio of the RSSImeasured power levels to determine the relative gain level adjustmentsof the front and rear amplification stages. In the described embodimentof the invention, if the power level of the signal and interference isapproximately equal to or slightly greater than the power level of thesignal alone, then the first amplification stages are set to a highvalue and the second amplification stages are set to a low value.Conversely, if the power level of the signal and interference issignificantly greater than the power of the signal alone, therebyindicating significant interference levels, the first amplificationstages are lowered and the second amplification stages are increasedproportionately.

Circuitry portion 304B includes low pass filters for filtering I and Qcomponent frequency correction signals and mixer circuitry for actuallyadjusting LO signal frequency. The operation of mixers and phase lockedloop for adjusting frequencies is known. Circuitry portion 304B furtherincludes JTAG (Joint Test Action Group, IEEE1149.1 boundary-scanstandard) serial interface (SIO) circuitry 344 for transmitting controlsignals and information to circuitry portion 304A (e.g., to controlamplification levels) and to a circuitry portion 304C (e.g., to controlor specify the desired frequency for the automatic frequency control).

A portion of the automatic frequency control circuitry that determinesthe difference in frequency between a specified center channel frequencyand an actual center channel frequency for a received RF signal isformed within the baseband circuitry in the described embodiment of theinvention. This portion of the circuitry includes circuitry thatcoarsely measures the frequency difference and then measures thefrequency difference in the digital domain to obtain a more precisemeasurement and to produce frequency correction inputs to circuitryportion 304B.

Finally, radio circuitry portion 304C includes low pass filtrationcircuitry for removing any interference that is present after basebandprocessing as well as amplification, mixer and up-converter circuitryfor preparing a baseband signal for transmission at the RF.

FIG. 4 is a functional schematic diagram of an automatic frequencycontrol (AFC) circuit formed according to one described embodiment ofthe invention. The AFC circuit of FIG. 4 comprises an RF signalprocessing portion 360 and a baseband signal processing portion 362.Generally, portion 360 is for adjusting an LO signal frequency. Portion362 is for determining the difference in center channel frequenciesbetween the received RF and the expected frequency value for thereceived signal.

An analog-to-digital converter (ADC) 364 is used to convert the receivedsignal from analog to digital. ADC 364 is coupled to receive an RFsignal that has been down-converted to produce a digitally convertedsignal to frequency synchronization circuitry 368 that measures thefrequency difference in a coarse degree of resolution. Digital frequencycontrol circuitry 366 performs its measurements and calibration in thedigital domain and provides its results to frequency synchronizationcircuitry 368 to adjust the frequency difference of frequencysynchronization circuitry 368 with a fine degree of resolution.

Frequency synchronization circuitry 368, as a part of determining thedifference in center channel frequency for the received signal and anexpected value, receives and interprets a pilot signal that defines theexpected center channel frequency. Accordingly, after measuring theactual center channel frequency of the received RF, frequencysynchronization circuitry 368 is able to determine the frequencydifference. Frequency synchronization circuitry 368 then produces asignal defining the difference in center channel frequency for thereceived signal and an expected value to a signal generator 370. It isunderstood that the pilot channel is transmitted as a part of standardwireless network communication protocols for signal control andsynchronization purposes.

Signal generator 370, upon receiving the difference in center channelfrequency for the received signal and an expected value, producesquadrature phase shift keyed (I and Q) outputs for the receivedfrequency difference (reflecting a frequency adjustment amount) to apair of digital-to-analog converters (DACs) 372. The analog outputs ofthe pair of DACs 372 are then passed to low pass filters 374 and arethen up-converted to the RF. The I and Q RF signal components are thenproduced to mixer circuitry 376 that also receives a specified inputfrom phase locked loop (PLL) circuitry 378 to produce a received RFhaving a specified center channel frequency. It is understood that mixercircuitry 376 (including PLL circuitry 378) further receives controlsignals from baseband processing circuitry (not shown in FIG. 4)specifying the expected center channel frequency that is specified inthe aforementioned pilot channel.

FIG. 5 is a diagram that illustrates the relative difference between aradar signal waveform and an 802.11 wireless LAN waveform signal.Generally, it may be seen that radar signal pulses have a significantlyhigher magnitude than the 802.11 wireless LAN waveform signal.Additionally, radar pulses have a much shorter pulse width. In theexample shown, each radar pulse has a 1 microsecond pulse width and isspaced apart by approximately 1 millisecond (though the figure is not toscale). The 802.11 wireless LAN waveform signal, in contrast, has aperiod that equals at least 40 microseconds and can equal 3milliseconds. Thus, the waveform of the radar pulses and the 802.11wireless LAN signal are notably different, however, which facilitatesdetection by a radar detection block as disclosed herein.

Continuing to examine FIG. 5, it may be noted that the radar pulses comein blocks. While 5 pulses per block are shown, it is understood thateach block of pulses may have a different number of pulses. Generally,the radar pulses are in the 5.25-5.75 GHz frequency band having a 1 to10 MHz bandwidth. The 802.11 frequency bands that are approximate to thefrequency band of radar range from 5.15-5.35 MHz and from 5.725-5.825MHz. Accordingly, it may be seen that an overlap exists between thesetwo frequency bands for 802.11 with the frequency band for the radarpulses.

FIG. 6 is a diagram illustrating two groups (blocks) of pulses of aradar signal. Generally, it is a goal to detect a radar signal before asecond group of pulses is received. Accordingly, as may be seen for thefirst group of pulses, a radar detection block, and more particularly, astate machine of the radar detection block in conjunction with aprocessor, must be able to detect and determine that a radar signal ispresent from the five pulses shown of the first group of pulses in FIG.6. As is understood, a common characteristic of radars is that the radarantenna oscillates or rotates thereby radiating any one point in spaceonly for a limited time while the point in space is within a beam angleof the radar antenna. Accordingly, even though the radar continuouslyproduces radar pulses, they are seen by the receiver in groups and arenot seen as the radar antenna sweeps away.

As may further be seen, a plurality of threshold levels is defined.These threshold levels are used by the state machine and the processorto determine that the radar signal is present. The logic for concludingthat a radar signal is present in relation to the pulses will bedescribed in greater detail below. Generally, it may be seen that thefirst threshold level (TH₀), in one embodiment of the invention, isdefined to be within the range of −80 decibels per meter (dBm) relativeto a milliwatt. A second threshold (TH₁) is defined at −63 dBm.

The thresholds TH₀ and TH₁ are chosen in order to meet the requirementsfor radar detection sensitivity and to avoid false alarms and thus maybe modified so long as this design goal is considered for a particularradar having known signal characteristics. In a first embodiment,absolute thresholds are used. The choice of TH₀ is made by firstestimating the probability of detection and probability of false alarmfor the expected environment. In an ideal environment (known radarsignals in additive white Gaussian noise (AWGN) the computation isstraightforward. However, in practice, the thresholds will be adjustedin the described embodiments of the invention in a dynamic fashion inorder to maximize radar detection performance.

FIG. 7 is a diagram that illustrates the measurement of rise time andfall time of the pulses of the radar signal. More specifically, a timeto is defined as being when a rising pulse crosses the first thresholdTH₀. A second time value t₁ is defined when the pulse crosses the secondthreshold TH₁. A third time period is defined, t₂, as being the timewhen a falling pulse crosses the TH₁ threshold. Finally, a fourth timeis defined as t₃ whenever the falling pulse crosses threshold TH₀. Bymeasuring the rise and fall times, the state machine and processorexecuted logic, in the described embodiment, may better determinewhether a radar pulse was detected. The logic portion performed by theprocessor may also be implemented with hardware such as applicationspecific integrated computer logic, field programmable gate array logic,etc. These crossings of TH₀ and TH₁ enable a processor, state machine orother logic performing pulse detection operations to measure a risetime, a fall time, a pulse width and a total signal period. Thesemeasured signal characteristics make up what is referred herein also aspulse information that is entered within a table for evaluation tofacilitate determination as to whether a radar signal is present.

FIG. 8 is a functional block diagram of a portion of a radio transceiver400 according to one embodiment of the present invention. Initially, anRF signal received at an antenna is coupled to a low noise amplifier402. Low noise amplifier 402 produces amplified RF to mixers 404 and406. Mixer 404 mixes the amplified RF with a local oscillation todown-convert the RF to a baseband frequency signal to create adown-converted I channel signal. Similarly, mixer 406 mixes the receivedamplified RF signal with a phase shifted local oscillation, wherein thephase is shifted by 90°, to produce a down-converted Q channel signal.Low pass filters 408 and 410 are coupled to receive the down-converted Iand Q channel signals, respectively, to produce filtered I and Q channelsignals to a pair of variable gain amplifiers 412 and 414, respectively.Variable gain amplifiers 412 and 414 further receive gain controlsignals from an 802.11a physical layer digital signal processor 416.Responsive to the gain control from processor 416, variable gainamplifiers 412 and 414 provide a corresponding amount of gain to thefiltered I and Q signals and produce amplified I and Q signals toanalog-to-digital converters 417 and 418. Analog-to-digital converters417 and 418 then convert the amplified I and Q signals to digital toproduce incoming I and Q digital signal streams to processor 416.

Radio transceiver 400 of FIG. 8 further includes a radar detection block420 that is coupled to receive the incoming I and Q digital signalstreams to detect the presence of a radar signal. Upon detecting thepresence of a radar signal, radar detection block 420 produces controlsignals to processor 416 to prompt processor 416 to suspendcommunications over frequency bands that overlap with the radarfrequency bands. The operation and structure of radar detection block420 is described in greater detail below.

FIG. 9 is a block diagram of a radar detector block for use in an802.11a receiver according to one embodiment of the invention. Thiscorresponding 802.11a receiver for the radar block of FIG. 9 is a directconversion type receiver, although the invention is applicable to asuper-heterodyne receiver as well. (Both are commonly used for 802.11type wireless LANs.) The inputs to the radar detection block of FIG. 9are the outputs of the analog-to-digital converters (ADCs) that aretapped off and produced to the radar detection circuit (as shown in FIG.8, for example). The input signals produced by the ADCs are digitalsignals that are sampled at a sufficient rate and with a sufficientnumber of bits to facilitate use for radar detection. For example, a 40MHz sampling rate at 8 bits of precision is adequate to detect radarsystems in an 802.11a environment.

As was shown in relation to FIG. 8, radar detection block 420 receivedthe incoming I and Q digital signal streams produced by ADC 417 and ADC418. As may be seen in FIG. 9, the incoming I and Q digital signalstreams are received by mixers 422 and 424. Mixers 422 and 424 areoperatively coupled to receive each of the incoming I and Q digitalsignal streams twice to square each of the incoming I and Q digitalsignal streams. Accordingly, mixer 422 produces a squared I digitalsignal stream, while mixer 424 produces a squared Q digital signalstream. The squared I and Q digital signal streams are then produced toan adder 426 that sums the two squared signals to produce a summed I andQ squared signal stream to a switch 428.

In a first position, the summed I and Q squared signal stream isproduced to moving average filter 430 that calculates a moving averageof the summed I and Q squared signal stream. Moving average filter 430then produces a moving average value to decibel conversion block 432,which converts the moving average value produced by filter 430 todecibel units.

Whenever switch 428 couples moving average filter 430 to adder 426, aswitch 438 couples the output of decibel conversion block 432 to athreshold comparison state machine 440. Accordingly, the moving average,in decibels, is produced to threshold comparison state machine 440 foranalysis as will be described below. Whenever switch 428 couples adder426 to a decibel conversion block 434, however, the summed I and Qsquared signal stream is produced to decibel conversion block 434 whichproduces the summed I and Q squared signal stream in decibels to asubtractor 436. Subtractor 436 is further coupled to receive andsubtract a receiver gain setting from the summed I and Q squared signalstream in decibels. The output of subtractor 436 is then coupled, byswitch 438, to threshold comparison state machine 440. Thresholdcomparison state machine 440 operates as described below to providepreliminary analysis of the detected power levels produced either bydecibel conversion block 432 or subtractor 436 to a processor 442. Radardetection logic 444 within processor 442, then analyzes the preliminaryanalysis received from threshold comparison state machine 440 todetermine whether a radar signal has been received.

This circuit of FIG. 9 computes the received power and applies either nofiltering (option 1 in which both switches are in the low position) or amoving average filter (option 2 in which both switches are in the upperposition). Option 1 is most effective for short pulse width radars whenno interference is present. Option 2 is most effective with longer radarpulses in interference that looks random as is shown in FIG. 10.

FIG. 10 is an illustration of signal waveforms for radar pulses and802.11a signals. In general, the radar detector will not have priorinformation concerning either the radar pulse width or interference.Consequently, in the described embodiment, logic drives switches 428 and438 to the lower position (option 1) unless an 802.11a frame is beingreceived (as determined during call setup signaling between an accesspoint and a wireless host or communication device in one embodiment ofthe invention). In the case of 802.11a communications, option 2 isemployed (the switches are toggled to the upward position as shown)during the duration of the frame.

When option 2 is employed during a received 802.11a frame, thethresholds are set to be relative to the average received power. Sincethe radar signal is typically a constant envelope signal, while theinterference is more like Gaussian noise, the moving average filter willhave the effect of improving the radar signal to interference powerratio by a factor of the square root of the filter length. Theimprovement is limited by the length of the radar pulse (i.e., maximumimprovement is when the radar pulse fills the moving average filter).Thus, the threshold level and filter length are jointly selected basedon the expected radar pulses length and the detection and false alarmprobabilities.

FIG. 11 is a functional block diagram of a moving average block asemployed in one embodiment of the present invention. The moving averagefilter effectively is an integrator and can improve the radar signal tointerference level for many types of radar signals. In the describedembodiment, four delay elements 446 are included coupled in series andhaving outputs that are further produced to an adder. A summed outputfrom the adder is then produced to a divide by “N” block 448. The valueof “N” in the divide-by-N block is equal to four in the describedembodiment since there are four delay elements. The number of delayelements and the divisor “N” may each be modified according toparticular requirements.

If it is assumed that the radar signal has a constant envelope, the Iand Q components then take the form:I(n)=A _(r) cos({overscore (ω)}_(r) nT+φ)Q(n)=A _(r) sin({overscore (ω)}_(r) nT+φ)where A_(r), the radar signal amplitude, and ω_(r), the down-convertedradar signal frequency, are constant (or approximately constant) duringthe radar pulse. The radar signal is zero outside of the received pulse.In constrast, the received 802.11a signal can be modeled as two Gaussiansignals:I(n)=G _(i)(n)Q(n)=G _(q)(n)The moving average filter of length n computes the following:$y = {{\sum\limits_{i = 1}^{k}I_{i}^{2}} + Q_{i}^{2}}$With an input signal that is composed of a radar signal embedded withinan 802.11a frame, the output of the moving average filter is:I(n) = A_(r)cos (ϖ_(r)n  T + φ) + G_(i)(n)Q(n) = A_(r)sin (ϖ_(r)n  T + φ) + G_(q)(n)$y = {{\sum\limits_{i = 1}^{k}{A_{r}^{2}\left( {{\cos^{2}\left( {{\varpi_{r}i\quad T} + \varphi} \right)} + {\sin^{2}\left( {{\varpi_{r}i\quad T} + \varphi} \right)}} \right)}} + {A_{r}^{2}{\cos\left( {{\varpi_{r}i\quad T} + \varphi} \right)}{G_{i}(i)}} + {G_{i}^{2}(i)} + {A_{r}{\sin\left( {\varpi_{r},{{i\quad T} + \varphi}} \right)}{G_{q}(i)}} + {G_{q}^{2}(i)}}$$y = {{k\quad A_{r}^{2}} + {\sum\limits_{i = 1}^{k}{A_{r}{\cos\left( {{\varpi_{r}i\quad T} + \varphi} \right)}{G_{i}(i)}}} + {G_{i}^{2}(i)} + {A_{r}{\sin\left( {{\varpi_{r}i\quad T} + \varphi} \right)}{G_{q}(i)}} + {G_{q}^{2}(i)}}$With the radar and signal model given above, y has a non-centralchi-square distribution with 2 k degrees of freedom. Thus, the relativeerror in the measurement of y is given by: $\begin{matrix}{{{Relative}\quad{Error}} = {\left( {{standard}\quad{deviation}\quad{of}\quad y} \right)/\left( {{mean}\quad{of}\quad y} \right)}} \\{= \frac{\sigma_{y}}{m_{y}}} \\{= \frac{\sqrt{{4k\quad\sigma_{wlan}^{4}} + {4{kA}_{r}^{2}\sigma_{wlan}^{2}}}}{{2k\quad\sigma_{wlan}^{2}} + {k\quad A_{r}^{2}}}}\end{matrix}$which decreases by a factor of the square root of k with increasing k.

FIG. 12 illustrates a threshold comparison state machine. This devicemeasures the time instants when the radar pulse crosses two thresholds.The output takes the form of 4 time measurements: start time (T₀), risetime (T₁), pulse width (T₂), and fall time (T₃). A set of the 4 timemeasurements is recorded for every complete cycle back to start.

The state machine operates as follows. It originates in the start stateand observes the incoming power estimate P. When P exceeds threshold P₀,the start time (T₀) is recorded and the state is advanced to Rising0.Once in Rising0, a counter is initiated to record the total time in thatstate (T₁). If the incoming power estimate drops below P₀, then thestate machine is reset and it returns to Start. As described herein, P₀and P₁ represent two threshold values used to identify a typical radarpulse. For example, the values of P₀ and P₁ may be set to TH₀ and TH₁ ofFIGS. 6 and 7.

When P exceeds the second threshold, P₁, the state machine advances tostate Rising1. The time it spends in this state is recorded in T2. WhenP drops below P₁, the state machine advances to Falling0. The time inthis state is recorded in T₃. If, while in the Falling0 state, P risesback up to P₁, then the state machine returns to the Rising1 state. T₂is then incremented by the contents of T₃ and T₃ is reset. This processof moving back and forth between the Rising1 and Falling0 states canhappen multiple times. After P drops below P₀, the state machine returnsto Start and the complete set of 4 time measurements are forwarded tothe processor.

The final radar detection decision is made by a programmable processoras shown in the embodiment of FIG. 9. In the embodiment of FIG. 8,however, the final radar detection decision may be made either in theprocessor or in radar detection block 420. Referring again to FIG. 9,processor 442, and more particularly, radar detection logic 444,periodically reviews the pulse data collected by the state machine 440,and compares it with the characteristics of known radar signals. One keycharacteristic for determining radar presence, however, is the pulserepetition frequency. Thus, the processor is operable to match multiplereceived pulses with the same relative spacing. When a sequence of thistype is observed, detection is declared. Otherwise, the pulse data isdiscarded, and the processor waits for new data. This multi-layerapproach helps minimize false detections, while maximizing the chancesthat actual radars are detected.

In the described embodiment of the invention, a processor receives theoutput of the state machine and logic defined therein (in radardetection block 444 of FIG. 9, for example) analyzes the output of thestate machine to determine whether a radar signal has been received. Itshould be understood that the following logic, as defined in block 444and executed by processor 442, may readily be formed in hardware asdescribed before.

The embodiments of the invention include a sequence of steps that aretypically executed on a programmable processor. FIG. 13 is a flowchartthat illustrates a series of steps that are performed according to oneembodiment of the invention. Generally, the invention includes measuringsignal characteristics to determine if a received signal has acharacteristic of a radar pulse and to further determine whether apattern of pulses is consistent with a radar pattern. More specifically,the invention includes determining whether a received signal hasexceeded a first threshold (step 450) and, when the first threshold isexceeded, a timer is initiated to track or measure a rise time (step452). The time is turned off and the rise time is determined when therising signal crosses a second threshold. Thus, the invention includesdetermining that the received signal has crossed the second threshold(step 454).

The invention further includes determining a pulse width. Thus, once thesecond threshold has been reached, the invention includes initiating asecond timer to measure an amount of time above the second threshold(and therefore the pulse width) (step 456). The invention furtherincludes determining a received signal has fallen below the secondthreshold (step 458). The difference in time between the two crossingsof the second threshold define the pulse width of a received signal. Ifthe second timer is initialized to start counting from zero, the valueof the second timer represents the pulse width.

Once the second threshold is crossed in a downward position, meaning thereceived signal levels has crossed from above to below the secondthreshold, a third timer is initialized to track a fall time (step 460).Once the signal crosses the first threshold in the downward direction,the third timer is stopped and the fall time is determined (step 462),which fall is the time required for the signal level to fall from thesecond to the first threshold. Accordingly, the invention furtherincludes producing first, second and third timer values to logic fordetermining whether a radar pulse has been received (step 464). Finally,if a radar pulse has been received, the method of the embodiment of theinvention includes stopping all transmissions in frequency bands thatoverlap with radar frequency bands (step 466).

FIG. 14 is a flowchart illustrating a method for determining whether aradar signal is present according to one embodiment of the invention.For the described embodiment, it is assumed hardware of a radio receiveris continually filling a first in/first out (FIFO) with the pulseinformation. Moreover, in the described embodiment of the invention, theinventive method is repeated at periodic intervals of less than onesecond.

Initially, the invention includes receiving and detecting incomingpulses and placing the pulse information in a FIFO register (step 470).Detecting the incoming pulses includes measuring pulse characteristicssuch as rise time, pulse width and fall time. Thereafter, the inventionincludes producing pulse information to a processor and clearing theFIFO (step 472). Generally, this step includes loading pulse data (pulseinformation) into the programmable processor (in the describedembodiment) or other logic. In one embodiment, the pulse data is loadedby direct transfer such as by direct memory access (DMA).

After the pulse data is loaded, a table of pulse data is generated for aseries of pulses (step 474). If the total number of pulses is less thana specified number, processing is suspended (stopped) until thespecified number of pulses is listed within the table (step 476). Inaddition to adding pulse data to the table, the invention includesremoving pulse information from the generated table for any pulse havinga pulse width less than a specified minimum width amount and greaterthan a specified maximum width amount (step 478). In an alternateembodiment, pulse data is only placed within the table for furtheranalysis if the pulse width is within a specified range for a givenpulse. Accordingly, for this embodiment, the step of removing pulse datafor such a pulse is unnecessary. In either embodiment, however, pulsesthat are either too long or too short to be a radar pulse are removedfrom the table of pulse data entries. Typical radar systems have pulseswith a pulse width in the range of one to three microseconds.

The invention further includes determining whether a total number ofpulses is less than a specified number and, if so, stops furtherprocessing until the table has pulse data for a specified number ofpulses (step 480). In one embodiment of the invention, the specifiednumber is equal to six. Thereafter, the invention includes grouping aplurality of pulse data entries to enable detection of a specified radarpulse (step 482). In the described embodiment, the group of pulses aregrouped by time. More specifically, a nominal value of 210 millisecondsis used to group pulses. In the very specific embodiment, such agrouping is referred to as an epoch. The epoch or group length is set tobe long enough to perform radar detection processing (step 484) and tocover the burst lengths sufficiently long to detect desired radarsystems. This step takes advantage of a radar characteristic of radarsystems of pulses being transmitted and arriving in bursts. Although itis not known exactly how long the bursts will be for a radar, thenominal value of 210 milliseconds should be adequately long tofacilitate identifying a received radar signal. Finally, if a radarpulse has been received, the invention includes inhibiting or stoppingtransmission in frequency bands that overlap with radar frequency bands(step 486).

FIG. 15 is a flowchart of a method for performing radar detectionprocessing. In some cases, it is expected that a valid radar may not bedetected due to interference with one or more pulses. Accordingly, thegroup of pulses for which no radar was detected is evaluated for amissing pulse. Thus, for the grouped plurality of pulse informationentries (epoch), the invention includes generating a first list of pulserepetition intervals by subtracting a start time for a given pulse froma start time for an immediately preceding pulse for each pulse in thegroup (step 490). It is understood, of course, that this step cannot beperformed for the first pulse. Thereafter, the invention includesquantizing pulse repetition intervals with a specified granularity (step492). Generally, received pulse data has a degree of resolution that isnot necessary and may result in false determinations regarding radardetection conclusions. In one embodiment of the invention, the data isquantized to a resolution of 25 milliseconds and a smallest incrementalvalue. Thereafter, the invention includes removing all pulses not havinga pulse repetition interval value within a specified range (step 494).If the total number of pulses is less than a specified number (six inthe described embodiment) the process is stopped and is repeated for asubsequent grouped plurality of pulse information entries (step 496).

Once a group of pulses (epoch in the described embodiment) contains agroup of pulses that is equal to or exceeds the specified number ofrequired pulses (six in the described embodiment), the inventionincludes determining (by counting) which pulses have the most common andsecond most common pulse interval values in the group of pulseinformation entries (step 498). The method further includes determiningif a total number of most common pulse interval values is greater thanor equal to the specified number and therefore determining that a radarpulse has been detected (step 500). If the pulse train (group of pulses)does not suggest radar presence, the invention includes examining thepulse train to determine if the pulse train is missing a radar pulse(step 502). The specific steps for determining that a radar is presentnotwithstanding a missing pulse is illustrated in relation to FIG. 16.

If analysis of the pulse train for missing radar pulses does not suggestradar presence, the invention includes examining the pulse train todetermine if the pulse train includes an extra radar pulse (step 504).If a radar pulse is detected in any one of the prior steps, theinvention further includes suspending transmission in overlappingfrequency bands and classify radar by comparing frequency of pulses fromfirst list of pulse repetition intervals to known radar signals (step506). Finally, the invention includes continuing monitoring for radarand, once a radar signal is determined to not be present, resumingtransmission of communication signals in overlapping frequency bands(radar bands) (step 508).

FIG. 15 illustrated a method for determining whether a radar signal ispresent and whether transmissions in overlapping frequency bands shouldbe suspended. Within the steps of FIG. 15, there are two steps fordetermining whether a radar is present even if a pulse is missing (forexample, due to interference) or if there is an extra pulse (forexample, due to spurious noise or other noise source) in steps 504 and506, respectively. Each of these two steps, however, further includes aseries of steps for determining the same.

FIG. 16 is a flowchart illustrating a method for performing radardetection processing for missing pulses. FIG. 17 is a flowchartillustrating a method for performing radar detection processing forextra pulses. Referring now to FIG. 16, the method includes evaluatingwhether a 2*pulse interval of a most common pulse interval value isequal to a pulse interval of a second most common pulse interval value(step 510). Additionally, the invention includes evaluating whether the2*pulse interval of the second most common pulse interval value is equalto the pulse interval of the most common pulse interval value (step512). Also, the invention includes determining if the total number ofmost common and second most common pulses is greater than the specifiednumber (step 514). Finally, the invention includes determining that aradar pulse is present if any of the above three steps are true (step516). Generally, if any of these steps yields a true result, then aradar is present and detectable even if interference prevents receipt ofa radar pulse.

Another type of interference is the introduction of a signal thatappears to be a pulse. Thus, referring now to FIG. 17, the inventivemethod includes analysis for determining a radar signal is present evenin the presence of an extra signal appearing as a pulse. Morespecifically, the invention includes for a grouped plurality of pulseinformation entries, generating a second list of pulse repetitionintervals by subtracting a start time for a given pulse from a starttime for a pulse preceding an immediately preceding pulse (step 518).Thereafter, the pulse repetition intervals are quantized with aspecified granularity (step 520). The invention further includesremoving all pulses not having a pulse repetition interval value withina specified range (step 522). The remaining pulse intervals of a firstlist of pulse repetition intervals are then compared to the second listof pulse repetition intervals (step 524). Finally, the inventionincludes evaluating whether if pulse periods match from the comparison,and if the total number of pulses in the second list of pulse repetitionintervals is greater than a specified number, determining whether aradar is present (step 526).

FIGS. 18, 19 and 20 illustrate the generation of data that is utilizedin the described embodiments of the invention for determining whether aradar is present. More specifically, FIG. 18 illustrates the specificpulse data that is stored or evaluated. In the described embodiment, thepulse data is stored in tabular form and includes identification of thestart time, the rise time, the pulse width and the fall time for each ofa plurality of pulses. Based on the data of FIG. 18, FIG. 19 illustratessome of the aforementioned processing for determining whether a radar ispresent in view of a missing pulse. More specifically, a set of pulseintervals is defined between pulses and is mapped according to quantity.For example, the most common pulse interval is the pulse interval havinga value of (start time) E—(start time) A. The frequency of this pulseinterval is represented herein as “n1”. Such determinations are thenused as described herein for determining radar is present even if apulse is missing (was not received by the receiver). Finally, FIG. 20illustrates some of the processing relating to the presence ofadditional pulses and the method for detecting the presence of a radarin such cases. One important aspect of the table of FIG. 20 is that FIG.20 illustrates that start times and corresponding pulse widths are basedupon every other pulse. Accordingly, the pulse widths are twice as longas expected ordinarily. For example, the first row illustratessubtraction of a start time for pulse “A” from the start time for pulse“I”.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and detailed description. It should beunderstood, however, that the drawings and detailed description theretoare not intended to limit the invention to the particular formdisclosed, but, on the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the present invention as defined by the claims. As may beseen, the described embodiments may be modified in many different wayswithout departing from the scope or teachings of the invention.

1. A radio transceiver, comprising: radio front end for receiving,amplifying and down-converting and filtering a radio frequency (RF)signal to produce a low frequency received signal; analog-to-digitalconverter (ADC) operatively coupled to receive the low frequencyreceived signal, the ADC producing a digital low frequency signal;baseband processor coupled to receive and process the digital lowfrequency signal; radar detection circuit coupled to receive the digitallow frequency signal, wherein the radar detection circuit measuresmagnitude levels of received signals, rise time, fall time, and detectsa received radar pulse pattern and produces a corresponding controlsignal indicating whether a radar signal has been detected to thebaseband processor; and wherein the baseband processor does not producedigital signals whenever the control signal indicates that the radarsignal has been received.
 2. The radio transceiver of claim 1 whereinthe radio front end includes a low noise amplifier (LNA) for amplifyingthe received RF signal and down-conversion circuitry for down-convertingthe received and amplified RF signals to produce a down-convertedsignal.
 3. The radio transceiver of claim 2 wherein the down-convertedsignal comprises one of a low intermediate frequency (IF) or basebandsignal.
 4. The radio transceiver of claim 2 wherein the down-convertedsignal is produced to low pass filter circuitry for producing low passfiltered signals, wherein the low pass filtered signals are the lowfrequency signals produced to the analog-to-digital converter.
 5. Theradio transceiver of claim 2 wherein the down-converted signal isproduced as I and Q channel signals.
 6. The radio transceiver of claim 5wherein the radar detection circuit receives I and Q channel digital lowfrequency signals.
 7. The radio transceiver of claim 1 wherein the radardetection circuit measures signal magnitude rises above a plurality ofthresholds, rise time from a first to a second threshold, time above thesecond threshold, and fall time from the second to the first threshold.8. The radio transceiver of claim 7 wherein the radar detection circuitmonitors at least one of a magnitude, a pulse width and timing andtiming relationships of received pulses to determine whether a radarpulse has been received.
 9. The radio transceiver of claim 8 wherein theradar detection circuit comprises a state machine for determiningwhether the received pulse has a specified characteristic of a radarpulse.
 10. The radio transceiver of claim 8 wherein the control signalproduced by the radar detection circuit is a binary signal that is setto a specified logic state whenever the radar signal is detected. 11.The radio transceiver of claim 1 wherein the control signal produced bythe radar detection circuit includes threshold level and timinginformation wherein the baseband processor determines that a radarsignal has been detected.
 12. The radio transceiver of claim 12 whereinlogic within the baseband processor monitors at least one of themagnitude, the pulse width and the timing and timing relationships ofreceived pulses to determine whether a radar pulse has been received.13. The radio transceiver of claim 1 wherein the baseband processordetermines whether the pulse is a radar pulse based upon pulse width.14. The radio transceiver of claim 13 wherein the baseband processordetermines that the pulse is not a radar pulse if the pulse width isless than a specified amount.
 15. The radio transceiver of claim 13wherein the baseband processor determines that the pulse is not a radarpulse if the pulse width is greater than a specified amount.
 16. Theradio transceiver of claim 13 wherein the baseband processor determinesthat the pulse is not a radar pulse if a period between pulses is notapproximately constant.
 17. A radio transceiver, comprising: radio frontend for receiving, amplifying and down converting and filtering a radiofrequency (RF) signal to produce a low frequency received signal; analogto digital converter operatively coupled to receive the low frequencyreceived signal, the ADC producing a digital low frequency signal;baseband processor coupled to receive and process the digital lowfrequency signal; radar detection circuit coupled to receive the digitallow frequency signal, wherein the radar detection circuit furtherincludes: multiplication circuitry for receiving and squaring a lowfrequency digital signal; moving average filter coupled to selectivelyreceive an output signal produced by the multiplication circuitry, themoving average filter producing a moving average filtered signal; firstconversion block for converting a magnitude of the moving averagefiltered signal into decibel values; and a threshold comparison statemachine coupled to receive an output of the first conversion block indecibel values, the threshold machine for measuring rise time, falltime, and magnitude levels of received signals and detects a receivedradar pulse pattern and produces a corresponding control signalindicating whether a radar signal has been detected to the basebandprocessor; and wherein the processor is coupled to receives rise time,fall time, and magnitude levels of received signals from the thresholdcomparison state machine, and wherein the processor determines whetherthe radar signal has been received and, if so, inhibits transmissions onoverlapping frequency bands.
 18. The radio transceiver of claim 17wherein the radar detection circuit further includes a second conversionblock coupled to selectively receive the output signal produced by themultiplication circuitry, the second conversion block converting themagnitude of the moving average filtered signal into decibel values. 19.The radio transceiver of claim 18 wherein the radar detection circuitfurther includes a summing node for subtracting a receiver gain settingfrom the magnitude in decibel values of the output of the multiplicationcircuitry.
 20. The radio transceiver of claim 19 wherein the movingaverage filter and the first conversion block are coupled serially in afirst branch and the second conversion block and the summing node arecoupled in a second branch and wherein logic selects between the firstand second branch based upon whether a wireless local area network(WLAN) signal is being received.
 21. The radio transceiver of claim 20wherein the first branch is selected if the wireless LAN signal is beingreceived and the second branch is selected if the wireless LAN signal isnot being received.
 22. A method in a radio transceiver, comprising:initiating a first timer to track a rise time of a pulse; initiating asecond timer to track a pulse width of the pulse above a specifiedthreshold; initiating a third timer to track fall time; producing first,second and third timer values to a radar detection logic for determiningwhether a radar pulse has been detected.
 23. The method of claim 22wherein the radio transceiver processor stops transmitting in frequencybands that overlap with radar frequency bands if a radar signal has beenreceived.
 24. The method of claim 22 further including determining areceived pulse has exceeded a first threshold as a part of initiatingthe first timer.
 25. The method of claim 24 further includingdetermining a received signal has exceeded a second threshold as a partof calculating a rise time.
 26. The method of claim 25 further includingdetermining the received signal has exceeded a second threshold trackingpulse width.
 27. The method of claim 26 further including determiningthe received signal has fallen below the second threshold as a part ofcalculating the fall time. 28 The method of claim 27 further includingdetermining the received signal has fallen below the first threshold asa part of calculating the fall time.
 29. The method of claim 28 furtherincluding producing the rise time, the pulse width and the fall time tologic for determining if a radar pulse has been received.
 30. The methodof claim 29 wherein the logic is formed in hardware within the radardetection circuitry, the method further including determining if theradar signal has been received in the logic formed in hardware. 31 Themethod of claim 29 wherein the logic is formed within the basebandprocessor and is defined by computer instructions executed by thebaseband processor, the method further including the baseband processordetermining if the radar signal has been received.
 32. The method ofclaim 31 wherein the radar detection circuitry produces measuredparameters to the baseband processor to enable the logic within thebaseband processor to determine if the radar signal has been received.